To me, lag doesn’t matter if they’re the caster. If he had to cast a ritual that decided his powers for the day, that would still be magical.
I dig the ritual concept. My main idea in my own swordmage thread is based on using a warlock style chassis to provide a ritualist swordmage. They'd get less powerful "boom" spells, but be an encounter based full caster so that they can have weapon based cantrips. The flavor of their class features and spells would largely be that they are primarily a ritualist who has trained to combine their martial prowess seemlessly with ritualistic magic, energy channeling, and redirection of enemy magic.
Like, maybe an Aegis option would give Absorb Elements as a class feature, and when you absorb energy using it, you gain benefits beyond what the spell specifies, like increased speed, ac, etc, depending on the type of energy absorbed?
Definately new Rites as you level, like warlock invocations, that provide similar things. HOnestly, it would almost work as a variant warlock, but I think it might be less work to build from scratch using the warlock chassis.
The more subtle abilities can be fun, too. Ones who can see the ethereal...and strike those who reside therein? Ghost-killing is magic.
I once played a PC in a modern fantasy game who was a (mundane) deadeye shot and could move at full speed through even the most crowded space, even those that seemed impossibly tight, without touching any obstacles or betraying his passage beyond his footsteps. Magic made him both elusive prey AND relentless hunter.
I like stuff like that, too. I think a ritualist base, with options to inscribe sigils upon your body for always on abilities, would work well for that.